1. Field of the Invention
The present invention relates to a semiconductor device equipped with a capacitive element and its manufacturing method, and more specifically, to a semiconductor device equipped with a capacitive element with degradation of a capacitance insulation film caused by hydrogen suppressed and its manufacturing method.
2. Description of the Related Art
A manufacturing process of a semiconductor device is divided roughly into a so-called front end of the line (FEOL) in which various semiconductor elements are provided on a semiconductor substrate and a so-called back end of the line (BEOL). For example, capacitive elements (capacitors) mounted to semiconductor memory, etc. are formed in the front end of the line (FEOL).
Now, in a capacitor which has a general construction with a capacitive insulation film (capacitor insulation film) held between upper and lower electrodes, the capacitor insulation film is easy to come in contact with hydrogen or is susceptible to invasion of hydrogen in the capacitor insulation film. At the same time, in general, insulators used for a capacitor insulation film are likely to be formed by material susceptible to damage when it comes in contact with hydrogen or when hydrogen invades the inside. In addition, the condition in which hydrogen comes in contact with the capacitor insulation film or hydrogen invades the capacitor insulation film inside frequently occurs in the process associated with hydrogen. And the process accompanied by hydrogen is, in general, included in the back end of the line (BEOL). That is, in the back end of the line (BEOL) after the capacitor has once been formed, the condition in which the capacitor insulation film is susceptible to damage by hydrogen occurs.
When the capacitor insulation film is damaged by hydrogen, the film quality is deteriorated and the electric characteristics of capacitor are degraded. As a result, performance, reliability, quality, etc. of a semiconductor memory are degraded. And these influences of damage caused by hydrogen are more strongly exhibited in a ferroelectric film than a regular insulation film. That is, when the ferroelectric film is damaged by hydrogen, the ferroelectric properties are markedly degraded. Consequently, for example, when the ferroelectric film is damaged by hydrogen in ferroelectric random access memory (FeRAM), which is equipped with ferroelectric capacitors whose capacitor insulation film is formed by ferroelectric substances, electric properties of ferroelectric capacitors are markedly degraded. As a result, performance, reliability, quality, etc. are markedly degraded.
In order to prevent degradation of ferroelectric characteristics of a ferroelectric film by hydrogen as described above, several constructions to block hydrogen for a capacitor insulation film has been proposed. Such a construction is called, for example, a hydrogen barrier construction, etc.
For example, in the technique disclosed in Jpn. Pat. Appln. KOKAI Publication No. 7-273297, the ferroelectric capacitor has surfaces covered with a hydrogen barrier film, except for connections (contact section) between the upper electrode and the contact plug for upper electrode and the main surface (lower surface of lower electrode) on the side connected to the contact plug for lower electrode. However, with this construction, the surface of the contact plug for upper electrode is not covered with the hydrogen barrier film. Furthermore, no hydrogen barrier film is provided between the upper electrode and the contact plug for upper electrode. Consequently, with this configuration, it is extremely difficult to block hydrogen which intends to intrude (mix) into the ferroelectric capacitor inside via a contact hole for upper electrode when a contact plug for upper electrode is provided in the contact hole for upper electrode in the back end of the line after the ferroelectric capacitor has been formed in the manufacturing process. Consequently, in the back end of the line, the capacitor insulation film is susceptible to damage by hydrogen.
In this way, with the hydrogen barrier construction proposed to date, it has been difficult to satisfactorily prevent damage of hydrogen to the capacitor film not only when the capacitor insulation film is formed with ferroelectric substance but also when the capacitor insulation film is formed by regular insulation material.